Triple knuckle extension



FIG. 1 is a top perspective view of the claimed design for a triple knuckle extension;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The article is shown with a symbolic break in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design. 

CLAIM The ornamental design for a triple knuckle extension, as shown and described. 